Numerous industrial processes use acids in their processing that dilute or contaminate the acid with water. These contaminated acids are commonly referred to as “spent acid”. Industrial chemical and petroleum processes are prime examples. Many of these processes require purification or regeneration of the process acid to remove impurities, and reconstitute the acid which often require costly processing. Handling spent acid also raises safety and environmental concerns. Accordingly, there is ample need for a separation process to efficiently and effectively reconstitute the acid and, where needed, remove impurities from process contaminated acids, to restore the acid to or near its original process specification. It would also be beneficial if that process could be deployed “in situ” with the process that produced the spent acid. The present invention is directed to a polymeric membrane that is suitable for use in regenerating process acids. The polymeric membrane withstands the acid environment and preferentially diffuses the water over the retentate acid. The process can be used “in-situ” with common chemical petroleum and petrochemical processes. Though particularly described hereinafter in relation to use in a petroleum processing stream, the polymeric membrane has application to varied acid/water separations.
Acids are widely used in industrial chemical and petroleum refining applications that require acid “regeneration,” which generally means removal of water from the spent acid to restore the acid to, or near to, its original process specification or requirements. An exemplary acid use to illustrate the present invention is sulfuric acid, which is used in a number of chemical, petrochemical and petroleum refining processes.
Sulfuric acid is widely used in industrial chemical and petroleum refining processes. Depending on the use, commercial “fresh” acid is typically supplied in strengths of 70-99.5 wt % sulfuric acid with the remainder typically being water. Many uses generate a waste or spent acid stream containing a higher percentage of water. This spent acid stream is typically reprocessed to remove the water. Incineration and reconstitution of the sulfuric acid is conventionally used to remove the water and other contaminant organic material.
Conventional methods for spent acid regeneration involve generally combustion of the spent acid to form sulfur dioxide, conversion of the sulfur dioxide to sulfur trioxide, and absorption of the sulfur trioxide in water. While this technology is widely used to produce high strength acid (>98 wt % H2SO4), it is capital intensive. Thus, it is usually more economical for low volume users of sulfuric acid to transfer spent sulfuric acid by various means such as rail, truck, ship, or pipeline to a central regeneration facility rather than construct their own facilities for acid regeneration. Freight costs can be a significant part of the total costs for regenerating spent acid.
Sulfuric acid can also be regenerated from about 70 wt % H2SO4 to about 85 wt % or about 96 wt % sulfuric acid by using evaporation with one or two stages. The evaporation method is highly energy intensive as the acid/water mixture must be heated to a high temperature to vaporize the water. It also requires special materials such as glass lined vessels and tantalum heaters to prevent corrosion. An improved, less expensive method for regenerating spent sulfuric acid is needed, preferably a method that may be employed in situ.